Is the U.S. rate of childhood obesity reversible?The American Stroke Association's annual conference in February revealed some profoundly disquieting news: Since 1994, there has been a roughly 30 percent increase in the rate of stroke among children age 5 to 14. The researchers who conducted this study readily acknowledge they don't know for sure why stroke rates—which are declining in adults over age 50—are on the rise in children. The study, a review of hospitalization records between 1994 and 2007, was designed to show what was happening but not why.

But that does not preclude some educated guesses, by the researchers and the rest of us. The authors' best guess, and mine, is that the declining age of stroke patients is directly related to epidemic obesity and diabetes and rising rates of hypertension among children. We don't know that with certainty, but with the stakes this high, do we really want to wait for more data?

This tension between certainty and action points to a fundamental difficulty in applying science-based solutions to public-health problems. Science, which serves us admirably in general, is reductionist. It looks at the impact of one or a few specific factors on a given health outcome. So when the answer lies in large-scale causes rather than discrete ones—in the broad sweep of history rather than a particular causal sequence—the insights of science may founder.

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These limitations are important to keep in mind when it comes to dealing with the urgent problem of childhood obesity. Science has not given us a definitive answer as to what has caused the upswing in obesity rates, and perhaps it can't—because there is no one thing to blame. Looking for a specific cause may be an attempt to indict a snowflake in a lethal avalanche. Everyone is innocent, but all are guilty.

Similarly, everything about modern living may be the cause of epidemic obesity—and thus the cause may be a bit too large to fit within the customary field of scientific vision. But if science can't hand us a single, definitive cause for childhood obesity, it must face the same shortcoming when it comes to the cure.

Looking for a particular fix for epidemic obesity is rather like attempting to determine which sandbag in a levee stops the flood. Any one thing we do to turn this morbid tide is just one sandbag. But when we have done enough things right, we will have built a levee capable of damming the flood waters. To solve the problem, we need as many good, strong sandbags as possible.

That's why it was so helpful to get the hive mind focused on this issue, and why it's so important that we continue attacking the problem on multiple fronts, even as particular solutions emerge as favorites. We need a comprehensive system of reforms in knowledge, behavior, policies, and the environment. We need nutrition education and physical education in schools. We need to have physical-activity breaks as a standard part of the workday. Every neighborhood needs to provide recreational facilities and sidewalks, and new neighborhoods should be designed so that it makes sense to get around in them by foot rather than by car. We need social engineering to give us back time to prepare food at home or ways to eat out that offer good nutrition at low cost.

We need to make it a social norm to take the stairs rather than the elevator (or at least make the stairs more fun). We need to overhaul the food supply and eliminate the category of "junk" food. We need to subsidize the sale of fresh fruits and vegetables. Better still, we need to link subsidies to an objective measure of nutrition. We need truth in advertising and controls on food marketing to children.

We need to educate families about how to practice good nutrition and physical activity together. It should once again be possible for children to walk and bike to school. The nutritional quality of foods should be reliably discernible at a glance (something I've been working on). We need clinicians who provide effective lifestyle counseling so they are consistently part of the solution and never part of the problem.

We need policies, practices, and programs that make eating well and being active the daily routine and cultural norm. And we need to make it easy for people to convert their commitment to the cause into a constructive contribution.

We should suppress any inclination to look for a quick fix; there will be none. But we should equally suppress any tendency to let the arduous task of building the levee dissuade or intimidate us. Rome was rebuilt in the time of Hadrian brick by brick; we can reverse the tide of childhood obesity in our modern world one well-placed sandbag at a time.

So here's to the end of this Hive and to the continuation of its mission. We will need as many good ideas as we can get our hands on. Nothing we do will fix childhood obesity. But everything we do right … just might.